1. Field of the Invention
The present invention concerns a fuel injection control method for diesel engine and a regeneration control method of exhaust post-treatment apparatus.
More precisely, it concerns an engine fuel injection control method for exhaust gas temperature rising of a diesel engine or for oxygen decrease in the exhaust gas, and a regeneration control method on an exhaust gas post-treatment apparatus such as continuous regeneration type diesel particulate filter system of the like for purifying the exhaust gas by trapping particulate matter, using these fuel injection control methods.
2. Detailed Description of the Prior Art
In the recent fuel injection control technology, as shown in FIG. 14(a), a multistage injection technology has been developed actively by increasing the number of injections, in order to retard the rising of the injection quantity when starting the fuel injection, because, in the accumulator type fuel injection apparatus of the like, in the course of main injection, the amount of emission of nitrogen oxides (NOx hereinafter) or particulate matter (PM: particulate: PM hereinafter) increases, if it is injected at once, as the rate of injection in respect to the crank angle is high from the beginning, the amount of fuel to be injected into the combustion chamber increases suddenly, and the fuel blows in at a stretch.
Besides, a fuel injection control technology has been developed for performing an after injection with a small interval after the main injection, and accelerating the mixture of fuel injected in the main injection and sucked air, by intermediated of the energy of this after injection, as shown in FIG. 14(b), in order to early terminate the combustion of fuel of the main injection and thereby reduce PM.
In addition, the fuel injection mode control method of Japanese patent application Kokai publication No. 2000-97077 proposes to improve the ignitionability of the fuel injection, by adopting a multistage injection mode for performing a multistage pilot injection, as shown in FIG. 14(c), during the engine start.
These fuel injection control technologies aim at reducing the emission of NOx and PM, terminating the fuel combustion rapidly, and converting the thermal energy into engine output as much as possible, as a result, the exhaust gas temperature lowers.
On the other hand, as for the diesel engine, in recent years, an exhaust gas post treatment apparatus provided with oxide catalyst and NOx catalyst for elimination of hazardous constituents such as PM, NOx, SOx and others emitted from the engine and further a diesel particulate filter (DPF for Diesel Particulate Filter: PDF hereinafter) for catching PM is arranged in an exhaust passage.
The filter for directly catching this PM includes ceramic monolithic honeycomb shape wall flow type filters, fiber shape type filters where ceramics or metals are formed into fiber, or others, and the exhaust gas purification apparatus using these DPF are installed in the middle of the engine exhaust pipe, cleans and emits the exhaust gas.
However, this filter for catching PM is clogged along the trap of PM, and the exhaust gas pressure (exhaust gas pressure) rises as the trapped amount of PM increases, it is required thereby to eliminate PM from this DPF, and therefore, several methods and systems have been developed.
Among them, there is a system for eliminating PM by combustion through the heating of the filter with an electric heater or a burner, or back washing by flowing the air in the opposite direction; however, in the case of these systems, the fuel efficiency deteriorates, because PM is burned by supplying heating energy from outside, and the regeneration control is difficult.
In addition, in the case of adopting these systems, often two lines of exhaust passage provided with DPF are installed, PM trap and filter regeneration are repeated alternately, thereby tending to increase the size and cost of the system.
In order to cope with these problems, a continuous regeneration type DPF system as shown in FIGS. 15 to 17 have been proposed.
FIG. 15 shows an example of continuous regeneration type DPF system (NO2 regeneration type DPF system) by intermediate of nitrogen dioxide (NO2, hereinafter), and this continuous regeneration type DPF system 1A is composed of a wall flow type filter 3Ab and a oxidation catalyst 3Aa disposed upstream thereof. This upstream side oxidation catalyst 3Aa carrying platinum or the like oxidizes nitrogen monoxide (NO, hereinafter) in the exhaust gas to obtain NO2 (2NO+O2-->2 NO2) and this N02 oxidizes PM caught by the downstream side filter 3Aa to obtain, carbon dioxide (CO2, hereinafter) (2 NO2+C-->2NO+CO2) removing thereby PM.
Such this oxidation of PM by NO2 is performed with less energy barrier and at a lower temperature than the oxidation of PM by oxygen (O2, hereinafter), and thereby, with a reduced external energy supply, the filter can be regenerated by removing PM through oxidation, all the way trapping PM continuously by using thermal energy in the exhaust gas.
Besides, the continuous regeneration type DPF system (integrated NO2 regeneration type DPF system) 1B shown in FIG. 16 is an improvement of the system 1A shown in FIG. 15, in which oxidation catalyst 32A is applied on the wall surface of a filter 3B provide with wall flow type catalyst, and the oxidation of NO in the exhaust gas and the oxidation of PM by NO2 are performed on this wall surface. Thereby, the system is simplified.
Then, the continuous regeneration type DPF system (DPF system provided with PM oxidation catalyst) 1C shown in FIG. 17 applies precious metal oxidation catalyst 32A such as platinum (Pt) or the like and PM oxidation catalyst 32B to the wall surface of a filter 3C provide with wall flow type PM oxidation catalyst, and the oxidation of PM is performed on this wall surface from a lower temperature.
This PM oxidation catalyst 32B is a catalyst for direct PM oxidation by means of O2 in the exhaust gas, composed of cerium dioxide (CeO2) or the like.
For this continuous regeneration type DPF system 1C, PM is oxidized by NO2 using mainly a reaction of the oxidation catalyst 32A to oxidize NO to NO2 in a low temperature oxidation range (about 350° C. to 450° C.), PM is oxidized by a reaction of the PM oxidation catalyst 32B to oxidize directly PM by means of O2 in the exhaust gas (4CeO2+C→2Ce2O3+CO2, 2Ce2O3+O2→4Ce O2 or others) in a middle temperature oxidation range (about 400° C. to 600° C.), while PM is oxidized by O2 in the exhaust gas in a high temperature oxidation range (600° C. or more) higher than the temperature of PM combustion by O2 in the exhaust gas.
These continuous regeneration type DPF systems oxidize and eliminate PM while catching PM, by lowering PM oxidation temperature through the use of PM oxidation by catalyst or nitrogen dioxide.
However, even in these continuous regeneration type DPF systems, it is still necessary to rise the exhaust gas temperature to the order of 350° C., and the aforementioned reaction does not occur, and the filter can not be regenerated by PM oxidation in an engine operation state with a low exhaust gas temperature such as idling operation, extremely low load operation or the like, and PM continues to be accumulated in the filter, causing the problem of filter clogging.
For instance, in the idling operation, low speed or extremely low load operation when the engine break is operated on the downhill, the fuel is burned scarcely, a low temperature exhaust gas flows into the continuous regeneration type DPF apparatus, lowering the catalyst temperature and deteriorating the catalyst activity.
If the idling or extremely low load engine operation is sustained, PM trap progresses without supply of a hot exhaust gas that can oxidize and eliminate PM; therefore, PM can not be oxidized and eliminated while PM trap continues, resulting in the progress of filter clogging.
This progress of filter clogging increases the exhaust gas pressure and deteriorates the fuel efficiency and, moreover, when the exhaust gas pressure rises excessively along with the progress of filter clogging, the engine will stop, and if things come to the worst, it will develop to the disability of restart.
Especially, in the case of using a vehicle loaded with this continuous regeneration type DPF system for a home delivery service or the like dominated by urban area traveling, the engine runs mainly with a low exhaust gas temperature; therefore, it is often necessary to control in order to rise the exhaust gas temperature.
Therefore, it is planned to rise the exhaust gas temperature by retarding the injection timing, in the engine fuel injection; however, a misfire of injected fuel may be provoked if it is tried to rise the exhaust gas temperature by retarding considerably the injection timing, a limit occurs in the injection timing retarding angle, leading to the occurrence of a limit for the exhaust gas temperature rising, and the range of possible temperature rising comes to be reduced.
In addition to the regeneration of the filter for burning and eliminating PM caught in the aforementioned DPF, it comes to be required to rise, even momentarily, the exhaust gas temperature without increasing the engine output, or to generate temporally an exhaust gas of reducing atmosphere by reducing the oxygen concentration in the exhaust gas to almost zero, in order to activate by increasing the temperature of oxidation catalyst and NOx catalyst used for exhaust gas countermeasures, or to regenerate the occlusion substance of NOx occlusion reduction type catalyst.
In short, even temporally, a fuel injection control contrary, as the result, to the fuel injection control for lowering the exhaust gas temperature, by burning the fuel injected into the combustion chamber as soon as possible for increasing the engine output, as required in the prior art, comes to be required.
As one of methods for increasing the exhaust gas temperature and lowering the oxygen concentration, there is a method for retarding (delay) the main injection. In this retard of main injection, the more the timing is retarded, in short, the larger is the retard amount, the less the energy of the injected fuel is concerted in the engine output, and the more rises the exhaust gas temperature. Moreover, oxygen concentration in the exhaust gas can be reduced by increasing the fuel injection amount during the main injection.
In this retard of main injection, as the main injection which is generally performed neat the top dead center (TDC) is retarded, the pressure and temperature lower along with the distance from the TDC, only with the main injection, making the ignitionability difficult; in order to avoid this problem, a pilot injection is made near the TDC where the pressure and temperature are high, this fuel is burned to secure a kindling charcoal, so that the fuel of the main injection burns securely.
Nevertheless, concerning this main injection retard, there are problems of misfire, deterioration in output torque and fuel efficiency as explained below.
Concerning the misfire, it comes to be demanded to prolong the combustion time as long as possible, by increasing the interval between the pilot injection and the main injection that was not required for the prior art, in the retard of main injection, and misfire occurs if it is intended to increase the retard amount of the main injection, simply by an injection control only with the pilot injection and the retard of main injection, to meet with this demand.
Moreover, there is a case where the injection quantity is reduced in order to intend to optimize the main injection quantity in respect to the required exhaust gas temperature, in order to improve the fuel efficiency, the kindling charcoal becomes insufficient and flames off if the pilot injection quantity of that moment is constant.
Because of these problems of misfire, a limit is developed in the rising of exhaust gas temperature, and, the decrease of the oxygen concentration becomes unable to be achieved.
Also, as for torque output, when this retard control of main injection is performed, the engine output torque lowers as the combustion of the main injection is delayed, making impossible to maintain a high output torque, so there is a problem that this retard control of main injection can not be used in the case of desiring to maintain an output torque.
There, concerning the retard operation of this main injection, Japanese Patent Application No. 2000-291462 performs an auxiliary injection only once (second injection pattern), when the injection timing of the main injection is retarded largely, for increasing the exhaust temperature, and thereby the misfire is prevented.
However, if it is tried to maintain a combustion flame until the timing when the main injection is injected, only by a single sub injection, it becomes necessary to increase the fuel injection quantity in this sub injection, causing the problem of fuel efficiency deterioration.
At the same time, torque is generated by this sub injection, deteriorating the drivability. Moreover, a single sub injection limits the retard amount of the main injection, and the rising range of exhaust temperature will be reduced disadvantageously.